Levodopa is converted to a chemical called dopamine (DOE pa meen) in the brain. Symptoms of Parkinson's disease may be caused by low levels dopamine in the brain. Levodopa is turned into dopamine in the body.Carbidopa helps prevent the breakdown of levodopa before it can reach the brain and take effect.The combination of carbidopa and levodopa is used to treat Parkinson symptoms such as muscle stiffness, tremors, spasms, and poor muscle control.Carbidopa and levodopa is also used to treat Parkinson symptoms caused by carbon monoxide poisoning or manganese intoxication.